1. Field of the Invention
The present invention relates to three-dimensional multi-level semiconductor modules formed by alternately stacking sheet members and resin boards on which semiconductor chips are mounted and also relates to methods for fabricating the modules.
2. Description of the Related Art
With demands for size reduction and performance improvement of various electronic devices such as cellular phones and digital cameras, multi-level semiconductor modules formed by stacking and uniting a plurality of electronic components, especially semiconductor chips, have been proposed.
Methods for easily manufacturing such multi-level semiconductor modules at low cost have been proposed to date.
A conventional semiconductor module is formed by stacking, as one unit, a printed board on which a given circuit is formed, a semiconductor chip mounted on the printed board, and an interlayer member that has an opening capable of accommodating the semiconductor chip and includes a conductive bump capable of being connected to the circuit on the printed board. Such a conventional semiconductor module is fabricated by a method including the steps of: attaching protective films to both faces of an insulating base serving as an interlayer member; forming a through hole at a given position of the insulating base; filling the through hole with a conductive paste so as to form a conductive bump; peeling off the protective films; forming, in the insulating base, an opening capable of accommodating a semiconductor chip; and alternately stacking and bonding insulating bases and printed boards (see, for example, Japanese Unexamined Patent Publication No. 2002-64179).
With this method, a through hole is formed at a given position in an insulating base having both faces to which protective films are attached, the through hole is filled with a conductive paste, and then the protective films are peeled off, thereby forming conductive bumps protruding from the faces of the insulating base. Since the through hole penetrating the insulating base is filled with the conductive paste in this method, generation of a gap in a hole during the filling is avoided and connection reliability is enhanced, as compared to the case of using a via hole whose one open side is closed. In addition, electroplating that requires time and labor is unnecessary. Accordingly, a semiconductor module is easily fabricated at low cost.
Further, with miniaturization of electronic equipment such as IC cards and cellular phones, the density of semiconductor modules needs to be further increased and the thickness thereof needs to be further reduced. For this purpose, a semiconductor module having a stacked structure in which circuit boards on which semiconductor chips are mounted and interlayer members are alternately stacked and then are pressed with application of heat has been proposed (e.g., Japanese Unexamined Patent Publication No. 2003-218273). Specifically, circuit boards on which semiconductor chips have been mounted beforehand and interlayer members having openings capable of accommodating the semiconductor chips are alternately stacked with adhesive layers interposed therebetween, and then this stacked structure is pressed with application of heat. In this manner, the semiconductor chips are buried in the openings of the interlayer members so that electrical connection is established between the semiconductor chips through conductive posts formed on the interlayer members. With this method, the distance between the semiconductor chips is reduced, and failures caused by wiring resistance and inductance are reduced. As a result, electric signals are transmitted without delay and the density and function of the printed board are enhanced and the thickness thereof is reduced.